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Effects of Phosphorus and Potassium Fertilization on Septoria Glume Blotch of Wheat. B. M. Cunfer, Department of Plant Pathology, University of Georgia, College of Agriculture Georgia Station, Experiment 30212; J. T. Touchton(2), and J. W. Johnson(3). (2)(3)Department of Agronomy, University of Georgia, College of Agriculture Georgia Station, Experiment 30212; (2)Present address: Department of Agronomy, Auburn University, Auburn, AL 36830. Phytopathology 70:1196-1199. Accepted for publication 9 June 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1196.

A single application of phosphorus (P) and potassium (K) in the fall for wheat-soybean multiple cropping systems is a common practice that can result in excessive fertilization for wheat. The effects of applied and residual P and K and their interactions on Septoria glume blotch, lodging, and yield of wheat were evaluated in a minimum tillage system. In 1978 lodging increased as P levels increased but it was not entirely related to increased vegetative growth. Glume blotch severity was positively correlated with P rates (R2=0.76); 1,000-kernel weight and grain yield were negatively correlated with P rates, glume blotch, and lodging. In 1979, glume blotch ratings decreased at residual soil P levels from seven to 25 kg/ha (additional P and K were not applied in 1979) and then increased as residual soil P levels increased to 45 and 141 kg/ha. Lower plant height at the two lowest P levels probably contributed to greater glume blotch in these treatments. In 1979, 1,000-kernel weight was inversely related to glume blotch on heads. S. nodorum infection of seed was not significantly related to P, K, glume blotch, yield, or lodging in either year. S. nodorum in seed remaining on the soil surface during the summer declined to nearly zero by September and was not a significant source of inoculum for the next crop. Potassium and P K interactions did not affect any variable measured except grain yield in 1978 when increasing K rates lessened the detrimental effect of applied P. The results demonstrate that excessive P enhances glume blotch and reduces yield of wheat, but this relationship is not entirely related to lodging and vegetative growth.

Additional keywords: minimum tillage, multiple cropping.